A lot of the material on echo loaction by bats has been written by Leslie Kay. You might look for some of his materials. There was quite a bit on bats written in the 1960s as the Sonic Torch and Sonicguide were developed. Tom Tom Brennan KD5VIJ, CCC-A/SLP web page http://titan.sfasu.edu/~g_brennantg/sonicpage.html